1. Field of the Invention
The present invention relates to a solution treatment apparatus, a solution treatment method and a resist coating method, each holding a substrate such as a semiconductor wafer or the like on a substrate holding unit provided in a treatment cup, and performing solution treatment by supplying a treatment solution from a nozzle to the substrate and rotating the substrate.
2. Description of the Related Art
In a photolithography process on a semiconductor wafer (hereinafter, referred to as a “wafer”), resist coating treatment of forming a resist film on the front surface of the wafer is performed, and methods of the coating treatment includes, for example, a spin-coating method. In a resist coating apparatus employing the spin coating method has, for example, a spin chuck 11 holding the wafer W by suction, a rotation drive unit 12 rotating the spin chuck 11, a resist nozzle 15 supplying a resist solution to the wafer W, and a treatment cup 20 which surrounds the spin chuck 11 and has a waste solution path 13 and an exhaust pipe 14 connected to its lower portion, as shown in FIG. 17.
Further, in the treatment cup 20, an annular lower guide unit 21 inclined downward to the outside from below a peripheral edge portion of the wafer W, an annular upper guide unit 22 obliquely downward from near the peripheral edge of the wafer W with a gap therebetween, and an annular outer guide unit 23 above the upper guide unit 22, are provided. A gap between the lower guide unit 21 and the upper guide unit 22 forms an annular flow path 24. As shown in FIG. 17 and FIG. 18, the upper guide unit 22 has a plurality of openings 25 formed along a circumferential direction. The openings 25 allow a space surrounded by the outer guide unit 23 and the upper guide unit 22 to communicate with the annular flow path 24.
The exhaust pipe 14 is connected to a plant exhaust (an exhaust system including an exhaust path provided in a plant) via a damper 14a on the upstream side. The exhaust pipe 14 can exhaust an atmosphere in the treatment cup 20 at an exhaust rate at one of two stages such as a high exhaust (a state in which the exhaust pressure is high and the exhaust rate is high) and a low exhaust (a state in which the exhaust pressure is low and the exhaust rate is low), by the degree of opening/closing of the damper 14a. The high exhaust is set for a purpose of collecting mist at the time of discharging the resist solution, and the low exhaust is set for a purpose of collecting mist at the time of drying the resist. The reason why gas is exhausted at the low exhaust at the time of drying the resist is that exhaust of gas at the high exhaust can adversely affect the uniformity in film thickness.
Next, a resist coating process using the resist coating apparatus will be briefly described. In the resist coating apparatus, a downflow is formed by a fan filter unit (FFU) 17. In the resist coating apparatus, for example, the resist solution is applied from a resist nozzle 15 to a center of the rotating wafer W, and spin drying is then performed. In this process, a part of the resist solution scattered from the wafer W flows under its own weight down the lower guide unit 21, and is exhausted to the outside from the waste solution path 13. Besides, the resist become mist rides on a descending gas flow flowing through the openings 25 and a gas flow generated by the rotating the wafer W, through the annular flow path 24 and is sucked and exhausted from the exhaust pipe 14.
Incidentally, by supplying a solvent being a cleaning solution to a rear surface side of the wafer W while rotating the wafer W, a so-called rear surface cleaning has been performed conventionally. When performing the rear surface cleaning, it is requested to remove the resist attached to bevel portions on a front surface side and the rear surface side of the wafer W and accurately control a separation dimension between a peripheral edge of the resist film and a peripheral edge of the wafer W, that is, a cut width of the resist. Therefore, as described in Japanese Patent Application Publication No. 2008-277708, a technique is known in which a cleaning solution (solvent) is discharged to the bevel portion on the rear surface side of the wafer W from a nozzle fitted in an inner guide unit 21 below near the peripheral edge portion of the rear surface of the wafer W. When performing the bevel cleaning, the number of rotations of the wafer W needs to be set, for example, to a high rotation of about 2500 rpm in order to push up the discharged cleaning solution from the bevel portion on the rear surface side to a position slightly inside the peripheral edge on the front surface side of the wafer W through the bevel portion on the front surface side. A bevel cleaning nozzle 26 is fitted in the lower guide unit 21 as shown in FIG. 17. In this bevel cleaning process, the number of rotations of the wafer W is larger than that in the prior art, in order to cause the cleaning solution to reach the peripheral edge potion on the front surface of the wafer W.
On the other hand, the number of treatment cups 20 installed in a semiconductor manufacturing apparatus is increased with an improvement in production efficiency and thereby the total exhaust amount of the gas exhausted from a plurality of treatment cups 20 increases recently. Consequently, the plant power usage is pressed, and there is a concern that the increase adversely affects the environment. Further, in the resist coating apparatus, it is difficult to make the above-described exhaust system at two stages or more (for example, three stages such as a high exhaust, an intermediate exhaust, and a low exhaust) because of complication in control of the exhaust system. Therefore, it is forced to collect scattered resist mist by exhausting gas at the high exhaust at the time of discharging the resist solution and exhaust gas at the low exhaust in order to restrain the increase in exhaust rate except the time when discharging the resist solution (including the time of bevel cleaning).
Accordingly, in the bevel cleaning process, the number of rotations of the wafer W is increased, the flow speed of a gas flow generated by the rotation of the wafer W increases, and the exhaust rate from the treatment cup 20 is set to the low exhaust, whereby the air amount taken into the annular flow path 24 will exceed the exhaust capacity. However, a space of a vertical portion of the annular flow path 24 is set to be narrow in order to uniformly exhaust gas in a circumferential direction. For this reason, a part of the gas flow flowed into an inclined portion of the annular flow path 24 reversely flows upward from below through the above-described openings 25 as so-called excessive air as shown in FIG. 19, and flows to the outside from an opening of the treatment cup 20. In this event, the mist of the cleaning solution discharged from a discharge port 26a of the bevel cleaning nozzle 26 scatters to the outside of the treatment cup 20. As a result, the mist of the cleaning solution rides on the descending gas flow and reattaches to the front surface of the wafer W, and the attached portion causes a pattern defect. Further, since an outer edge of the wafer W and the upper guide unit 22 are close to each other in distance, the resist solution and the cleaning solution spun off from the wafer W can bump into an inner side wall of the upper guide unit 22 and bounce to the front surface of the wafer W and attach thereto.
In Japanese Patent Application Publication No. S59-127836, a resist coating apparatus is disclosed which has cylindrical shielding plates extending from an upper surface and a bottom surface of the treatment cup respectively to near an outer periphery of a wafer held on a spin chuck. However, the cylindrical shielding plates are provided essentially for the purpose of preventing bounce of the coating solution scattered from the rotating wafer, and therefore it is difficult to solve the problem of mist scattering to the outside of the treatment cup due to reverse flow of the above-described gas flow.